1. Field of the Invention
This invention relates to turbocharger control systems and more particularly to turbocharger control systems for controlling the operations of a turbocharger arranged in association with an automobile vehicle engine.
2. Description of the Prior Art
In FIG. 1 showing a conventional turbocharger control system, air which is communicated to a compressor 4 by means of an air passage 3 having an air cleaner 1 and an air flow meter 2 is compressed by a compressor 4, and is then supplied to surge tank 7 by means of passage 5 in response to the degree of opening of a throttle valve 6. After pulsations of compressed air are absorbed, the air is transmitted by means of passage 8 to combustion chamber 10 of the vehicle engine in response to opening movement of suction valve 9. The air within the chamber 10 is mixed with sprayed fuel, and the air-fuel mixture is ignited and combustion occurs in cooperation with compression operation of piston 11.
Exhaust combustion gases are transmitted to passage 13 by opening movement of exhaust valve 12 to thereby cause turbine 14 to rotate. This force of rotation causes the compressor 4 to rotate by means of shaft 15 of turbocharger T. The exhaust gases are then exhaused by means of passage 16. Passages 17, 18 and 19 are arranged between the passages 3 and 5 and relief valve device 20 is positioned therein. The valve device 20 includes housing 21, valve member 22, diaphragm 23 and spring 24, the valve member 22 being biased in its closed position by means of spring 24.
In such conventional system, when the driver suddenly releases the accelerator pedal driving under a high load or high speed conditions of the vehicle, throttle valve 6 is suddenly closed and therefore fluid pressure within passage 5 will be suddenly increased. The diaphragm 23 which continuously receives fluid pressure within passage 5 by means of passage 18 is now urged so as to be moved upwardly and valve member 22 is then urged to an open position against the biasing force of the spring 24. Accordingly, fluid pressure within passage 5 will be relieved by means of passages 19 and 17 to thereby reduce fluid pressure within passage 5 whereby damage to throttle valve 6 and the pipe defining passage 5 will be prevented. In such a conventional system, however, valve device 20 begins to operate only after fluid pressure within passage 5 exceeds a predetermined value. In other words, the valve device 20 is operated regardless of the speed of closing movement of throttle valve 6. Therefore, the responsiveness of operation of the valve device will be lessened.